Membrane Systems for Nitrogen Rejection
By
Kaaeid A. Lokhandwala, Andre Da Costa, Marc Jacobs and
Richard Baker
Membrane Technology and Research, Inc.
1360 Willow Road, Menlo Park, CA 94025
Website: www.mtrinc.com
Membrane Separation Mechanism
Permeability = Diffusivity * Solubility
(P)
(D)
(S)
Membrane Selectivity
P1
P2
=
D1 . S1
D2 . S2
MTR’s Rubbery Membranes Reject Nitrogen and
permeate hydrocarbon components
Glassy v/s Rubbery Membranes
Glassy Membranes
Fast Gas
Slow Gas
Nitrogen
Hydrogen
H2O
CO2
Ethane
Methane
Hexane
Propane
Rubbery Membranes
Fast Gas
Hexane
H2O
Slow Gas
Ethane
Propane
Methane
CO2
Nitrogen
Hydrogen
Membrane System Installations
Gas/Gas Separation Systems
H2/N2, CH4
~ 200 Units
O2/N2
~ 5,000 Units
CO2/CH4
~ 200 Units
Vapor/Gas Separation Systems
VOC/Air
Hydrocarbon/N2. CH4 ~ 100 Units
Glassy
Membranes
Rubbery
Membranes
MTR’s Composite Membrane
Selective
layer
Microporous
layer
Support
web
MTR Spiral Wound Cartridge
Module housing
Feed flow
Residue flow
Permeate flow
Residue flow
Feed flow
Feed flow
Spacer
Membrane
Spacer
Permeate flow
after passing through
membrane
Field Test Unit Process Diagram
N2 rich stream
Methane permeable membrane
J-T Valve
High pressure, N2
rich natural gas
Condensed
C3+ liquids/Water
Methane rich stream
Nitrogen Rejection Test System
Flow Capacity
Max: 0.2 MMSCFD
Operated: 0.10.1-0.2 MMSCFD
Pressure rating
Max: 1250 psig
Operated: 400400-600 psig
Temperature
Max: 135oF
Operated: 1515-50oF
Field Test – Inlet Gas Composition
Component
Methane
Ethane
Propane
Butane
Pentane and heavier
Water
Nitrogen
Composition
(mole%)
75.0
2.8
1.0
0.4
0.1
1.7
19.0
Comparison of Lab and Field Data
Methane-Nitrogen Selectivity
5
4
CH4-N2 3
Selectivity 2
1
0
-40
-20
0
20
40
60
80
100
o
Feed Temperature, F
field data from module
lab data from stamp
120
Long Term Separation Efficiency
Methane-Nitrogen Selectivity
4
3
CH4-N2
2
Selectivity
1
0
Jul-00 Sep-00 Nov-00 Jan-01 Mar-01
Date
Nitrogen Rejection – Application Envelope
• Inlet Nitrogen Content between 4 and 20 vol-%
• Inlet flow rate between 0.1 – 20 MMSCFD
• Discharge N2 specification between 4 and 8 vol-%
• Upgrading to Pipeline acceptability
• Upgrading fuel gas to meet BTU-Value for Burning
• Hydrocarbon Removal for Nitrogen Re-injection
Case 1 : Inlet N2 Content = 8 mol%
Waste gas
50 mol% N2
Feed gas
8 mol% N2
Fuel gas
15 mol% N2
Product gas
4 mol% N2
Two step process produces pipeline quality gas and fuel gas for process use.
Product gas compressor may be required to boost pressure to pipeline
pipeline
pressure.
Case 2 : Inlet N2 Content = 15 mol%
Compressor
Waste gas
65 mol% N2
Feed gas
15 mol% N2
Product gas
4 mol% N2
Fuel gas
25 mol% N2
Economic Analysis
Configuration
1
Process Characteristics
Parameter
Configuration
2
N2 in feed (%)
8
15
Feed flow rate (MMSCFD)
10
10
N2 in product gas
4
4
Methane recovery (%)
86
86
Methane in fuel gas (%)
87
75
Methane in waste gas (%)
50
35
Product gas flow rate (MMSCFD)
8.2
7.6
Power Requirements
Power required (Hp)
750
2,000
Capital and Operating Costs
Equipment cost ($000)
1,800
3,500
Processing cost ($/1000 scf)
0.27
0.56
• Processing Costs about
0.25 to 0.5 $/MCF are
very favorable
• Membrane system are
flexible and can be
used for various sites
and inlet gas
compositions
• Ideal for remote
continuous operation
without operator
attention
• Well suited for low flow
rate applications
Similar Applications – Fuel Gas Conditioning for
Gas Engines and Turbines
Designed for Offshore Installation
Main System Components
Membrane Modules/Housings
Filter Separator/Coalescer
Inlet and Discharge Valves
System Dimensions: 6 ft (W) x 8 ft (L) x 8 ft (H)
Location: Nigeria
Flow Capacity: 2.5 MMSCFD
Pressure rating 550 psig
Operating pressure: 220 psig
Feed hydrocarbon dewpoint: 82oF
Conditioned Gas Dewpoint: 20oF
Advantages of Membrane Systems
•
•
•
•
•
•
•
Simple passive system
High on-stream factor (typically > 98%)
Minimal or no operator attention
Small footprint, low weight
Large turndown ratio
Low maintenance
Lower capital and operating costs
Summary
Other applications in the Oil & Gas Industries for MTR’s ReverseSelective membranes
Gas:
Fuel gas conditioning, NG dewpointing, NGL Recovery, Natural
Gas Dehydration.
Oil:
Associated gas processing, Vapor recovery from storage tanks
and ship vents.